AO = Adjustable objective (paralax adjustment)
T.T. = Target Turret (allows easy and repeatable adjustments)
With the BSA or Golden Antler you will have a winner in my opinion. Good deals can be found on both but the BSA scopes are easier to find. No matter what brand you go with, make sure it is "airgun rated" so it will survive the recoil. Never tried a BSA on a D/W 1000 so I can't speak of the durability based on my own experiences.
Hope this helps. Getting late but will answer more tomorrow if you like.
Russ S.